From Haderuma Sima a line including the Miyako Retto to the East point of Miyako Sima and thence to Okinan Kaku, the Southern extremity of Okinawa Sima through this island to Ada-Ko Sima (Sidmouth Island) on to the East point of Kikai Sima (28°20' N) through Tanegra Sima (30°30' N) to the North point thereof and on to Hi-Saki (31°17' N) in Kyusyu.

On the North.

From Nomo Saki (32°35' N) in Kyusyu to the South point of Hukae Sima (Goto Retto) and on through this island to Ose Saki (Cape Goto) and to Hunan Kan, the South point of Saisyu To (Quelpart), through this island to its Western extreme and thence along the parallel of 33°17' North to the mainland.

The sea is called the East Sea in Chinese (東海; Dōng Hǎi), being one of the Four Seas of Chinese literature. There are three other seas, one for each of the four cardinal directions.[2]

Until World War II, the sea was referred to as 東支那海 (Higashi Shina Kai; "East Shina Sea") in Japanese. In 2004, official documents of the Japanese Foreign Ministry and other departments switched to the name 東シナ海 (pronounced the same), which has become the standard usage in Japan.

Common usage in Indonesia refers to the sea as Laut Cina Timur (East China Sea). This name was used officially by the Indonesian government until 2014, when Indonesia switched usage from the word Cina to Tiongkok instead; since then, the name Laut Tiongkok Timur become standard usage in Indonesia. Despite this, many Indonesian media outlets and publications continue to use the former sea name.

The dispute between the PRC and Japan concerns the different application of the 1982 United Nations Convention on the Law of the Sea (UNCLOS), which both nations have ratified.[5] China and Japan both claim 200 nautical miles EEZ rights, but the East China Sea width is only 360 nautical miles.[6] China proposed the application of UNCLOS, considering the natural prolongation of its continental shelf, advocating that the EEZ extends as far as the Okinawa Trough.[7][8] Its Ministry of Foreign Affairs has stated that "the natural prolongation of the continental shelf of China in the East China Sea extends to the Okinawa Trough and beyond 200 nautical miles from the baselines from which the breadth of the territorial sea of China is measured,"[7] which is applicable to the relevant UNCLOS provisions that support China's right to the natural shelf.[7][8] In 2012, China presented a submission under the UNCLOS concerning the outer limits of the continental shelf to the UN.[9][10] However, Japan claims about 40,000 square kilometers part of this territory as its own EEZ because it is within 200 nautical miles (370 km) from its coast, and thus proposed the Median line division of the EEZ.[6][11]

In 1995, the People's Republic of China (PRC) discovered an undersea natural gas field in the East China Sea, namely the Chunxiao gas field,[12] which lies within the Chinese EEZ while Japan believes it is connected to other possible reserves beyond the median line.[13] Japan has objected to PRC development of natural gas resources in the East China Sea near the area where the two countries Exclusive Economic Zone (EEZ) claims overlap. The specific development in dispute is the PRC's drilling in the Chunxiao gas field, which is located in undisputed areas on China's side, three or four miles (6 km) west of the median line proposed by Japan. Japan maintains that although the Chunxiao gas field rigs are on the PRC side of a median line that Tokyo regards as the two sides' sea boundary, they may tap into a field that stretches underground into the disputed area.[14] Japan therefore seeks a share in the natural gas resources. The gas fields in the Xihu Sag area in the East China Sea (Canxue, Baoyunting, Chunxiao, Duanqiao, Wuyunting, and Tianwaitian) are estimated to hold proven reserves of 364 BCF of natural gas.[15] Commercial operations began 2006. In June 2008, both sides agreed to jointly develop the Chunxiao gas fields,[14] but they have never been able to agree on how to execute the plan.[16]

Rounds of disputes about island ownership in the East China Sea have triggered both official and civilian protests between China and Japan.[17]

The dispute between PRC and South Korea concerns Socotra Rock, a submerged reef on which South Korea has constructed the Ieodo Ocean Research Station. While neither country claims the rock as territory, the PRC has objected to Korean activities there as a breach of its EEZ rights.